A variety of electronic devices use battery packs, including notebook computers, cellular phones, personal data assistants, and the like. A battery pack usually includes a number of battery cells. A variety of battery cell technologies are available, and new technologies are constantly being developed. One example commonly used today is the Lithium-ion battery cell. A Lithium ion battery cell can usually be safely charged up to about 4.2 volts, and can usually be safely discharged down to about 3 volts. Other battery technologies can provide different voltage ranges. Battery packs often include protection circuitry intended to maintain safe voltage ranges in the battery cells.
Depending on how battery cells are arranged, battery packs can support different voltage ranges and power requirements. For example, a battery pack commonly used in notebook computers may include six Lithium-ion battery cells, arranged in two parallel groups of three cells connected in series. Since voltages add when cells are connected in series, the voltage range for this three series, Lithium-ion battery pack may be about 12.6 volts (4.2 volts per cell) when fully charged, down to about 9 volts (3 volts per cell) when depleted. The voltage range can be increased or decreased by adding or removing cells in series. The number of parallel groupings determines how much current the battery pack can provide, with more parallel groupings able to support higher current rates or longer battery life at fixed current rates.
Many electronic devices can be designed to operate using any one of a variety of battery pack configurations. For example, some notebook computers have been designed to use three series battery packs, and some notebook computers have been designed to use two series battery packs. There may be trade-offs among different battery pack configurations. For example, some components, or loads, in a notebook computer may operate more efficiently, or be easier or less expensive to implement, using a two series battery pack, while other loads may operate more efficiently, or be easier or less expensive to implement, using a three series battery pack.